2.996/6.971 Biomedical Devices Design Laboratory

Lecture 5: Microprocessors I

Instructor: Dr. Hong MaSept. 26, 2007

Analogy: A Complex Machine with Lots of Knobs

Courtesy of NASA.

Microprocessor vs. PCs

• Microprocessors– Optimized to keep track of time– MSP430: 16MHz clock 62.5ns timing

• PCs– Optimized to process large amounts of data– Windows: ~100Hz timing– Linux: ~1kHz timing

• Timing accuracy can be leveraged for measurement functions

Trends in Sensor Architectures• Single processor distributed processors

The MSP430F2xx Family

• Optimized for low-power and versatility• Modern architecture, simple to program• Many peripheral devices – designed to not

require input from the CPU• Unified address space, no paging• Device emulates itself• Inexpensive development tools• Highly optimized code, designed for C compiler• Low cost, price >$0.50

MSP430F2xx Architecture

MSP430F2274 Pinout

Port Functions• Digital input• Digital output• Pulled-up / Pulled-down• Peripheral input / output• Interrupt on edge

Key: Locate the right control bits

Memory MapVon Neuman Architecture

Hardware(Switches and I/O)

“Software” (Instructions for flipping the switches)

Registers

Hex Numbers and MemoryMSP430 Memory

• 8-bit addressing resolution

The Header File (msp430x22x4.h)• Assigns aliases for registers• Specific to each processor sub-group

Bit-wise Operators

• Bit-wise “OR”: |– 1000 | 0101 1101

• Bit-wise “AND”: &– 1001 & 0101 0001

• Bit-wise “NOT”: ~– ~1001 0110

• Bit-wise “XOR”: ^– 1001 ^ 0101 1100

Assigning Individual Bits

• Assigning all 8-bits at once– P1OUT = 0xA7

• Assigning individual bits high– P1OUT |= 0x81

• Assigning individual bits low– P1OUT &= ~0x81

• Toggling individual bits– P1OUT ^= 0x81

How to Assign Individual Bits (Better)

• Assign all 8-bits at once– P1OUT = BIT7 + BIT5 + BIT2 + BIT1 + BIT0

• Assign individual bits high– P1OUT |= BIT7 + BIT0

• Assign individual bits low– P1OUT &= ~(BIT7 + BIT0)

• Toggling individual bits– P1OUT ^= BIT7 + BIT0

Configuring PortsMain(){...P1DIR |= BIT0 + BIT1 + BIT2 + BIT3 + BIT4 + BIT5; //Set output modeP1SEL |= BIT1 + BIT2;//Output Timer_A1 and Timer_A2P1REN |= BIT6 + BIT7;//Enable pull-up/down resistors for BIT6 and BIT7P1OUT |= BIT0 + BIT6//Output high on BIT0; Pull-up BIT6P1OUT &= BIT3 + BIT4 + BIT5 + BIT7//Output low on BIT3, BIT4, and BIT5; Pull-down BIT7...}

Next Topic: Clocks

MSP430 Clocking Scheme

Crystal Oscillators

• Extremely accurate – standard frequency tolerance = 20ppm

• Many frequencies: 20kHz – GHz• Real Time Clock: 32.768kHz• Requires 2 external capacitors• LFXT1 has integrated capacitors• Ceramic resonator

– Smaller, cheaper cousin– Frequency tolerance ~ 0.5%

Photo removed due to copyright restrictions.

DCO (Digital Controlled Oscillator)• 0 to 16 MHz• Fast start-up <1uS• ±3% tolerance• ±6% tolerance over

temperature• Factory calibration in

Flash• Good enough for

UART• Application: watch

Images removed due to copyright restrictions.

VLO (Very Low-power Oscillator)• 0.6µA typical at 25°C• ~12 kHz (min 4kHz, max 20kHz)• Can be calibrated using the DCO or XT• Applications: temperature monitor, blood

glucose sensor

Clock Module Diagram

Setting Up the Clock ModuleMain(){...// 16MHz xtal clock setup: MCLK = 16MHz, SMCLK = 2MHzBCSCTL1 = XT2OFF | XTS;// No XT2, LFXT1 in high frequency mode

BCSCTL2 = SELM1 | SELM0 | SELS | DIVS1 | DIVS0;// MCLK source is LFXT1;// SMCLK source is LFXT1;// SMCLK is divided by a factor of 8

BCSCTL3 = LFXT1S1;// Select integrated capacitors for 3-16MHz resonator...}

Clock Ports

Watch-dog Timer (WDT)• Designed to detect

– Software halting– Oscillator fault

• Active after device reset• “Kicking the dog” Reset the WDT• WDT runs down to 0 Processor reset• MSP430 WDT:

– Automatically switch clocks after failure– Password protected– Can be used as an ordinary timer

MSP430 WDT

WDTCTL = WDTPW + WDTHOLD;// Stop WDT

WDTCTL = WDTPW + WDTCNTCL;// Clear WDT

Structure of MSP430 Program

1. Declarations2. main()

1. Watch-dog timer servicing2. Setup clocking module3. Setup peripheral modules4. Enable interrupts5. Infinite loop

3. Subroutines4. Interrupt Service Routines (ISR)

Variable Types

Type Size Single-cycle instruction

char 8-bits Yes

int 16-bits Yes

long 32-bits No

float 64-bits No

Number Representation

• One’s Complement • Two’s Complement

//One’s comp. definitionunsigned char var1unsigned int var2

//Two’s comp. definitionsigned char var1signed int var2

Always explicitly define signed / unsigned !!!

Global Variables

• Global variables not always updated due to compiler optimization

//Declarationsunsigned char varvolatile unsigned char gvar...

Main(){...gvar=1;while(1);}

#pragma vector=USCIAB0RX_VECTOR__interrupt void UART_RX(void){gvar=2;...}

MSP430F2xx Address Space• 128kB address space• Unified memory map, no paging• F2274: 32kB flash, 1kB RAM

F2274: 08000h

Reset VectorInterrupt Vectors

Main()

ISR #1

ISR #2

ISR #3

Unused Flash Memory

0x8000

0xFFFF

0xFFFE

0xFFE0

UnaddressableSpace

Embedded Programming Styles

• Simple– Poll for events in main()

• Interrupt-driven– Code reside in the ISR– Used for handling a single interrupt source

• Event-driven– ISR sets flags for events– main()poll for flags and services them– Used for handling multiple interrupts sources

Components for Microprocessor Programming

• ICE – In-Circuit Emulator– Flash Emulation Tool (FET)– JTAG– Spy-Bi-Wire (2-wire JTAG)

• Bootloader– Rewrite flash via RS232– Password protected

• IDE – Integrated Development Environment– Editor, compiler, debugger

• Libraries for each microprocessor

Image removed due to copyright restrictions.

Brownout Detector and SVS• Brownout detector triggers a POR when supply voltage drops below 1.8V• SVS (Supply Voltage Supervisor) – Comparator-based (flash) ADC

Timer Related I/O

Communications Ports

Start / Reset Sequence

• PUC (Power Up Clear)• POR (Power On Reset)

Example C Code